Category maintenance

The whole of the last week has been spent trying to get to grips with the NSOutlineView provided by Cocoa. This gives you a standard leveled and expandable list, as shown in the window to the right. I've finally managed to implement to maintain Categories and SubCategories. No drag and drop yet but the basic functionality to allow users to view, insert, delete is all there. Even better it directly links in with all the underlying class datastructures, meaning that if you change the name of a category, say from "Cars" to "Vehicles" it will update all transactions from immediately. Surprisingly getting this all working wasn't exactly a trivial exercise. The documentation provided by Apple was a little terse and I resorted to plagiarising the only useful example I could find on the web from Big Nerd Ranch.
On a side note one thing I've started noticing about Cocoa is that is operates a quite different development for coding object events then all other development environments I've encountered. Visual Basic, Powerbuilder etc all allow you to object on an object in the interface builder, a push button for example, and directly let you write your code directly as an object property, in the "click" event for example. This means that the code tends to get scattered around the various objects that make up the window. In cocoa you write all your GUI code in a specific class for the window or application. I like this, in that it keeps the code together and hence makes debugging much easier. However for a complex window or application controller, I'm starting to find that the actual objective-c file starts getting enormous in size. Delegate methods get shared objects so every delegate needs to test what object it is that is sending the message. My AppController.m file is already up to 1,000 lines (including comments), and I've hardly started (gulp).